1. Field of the Invention
The invention relates generally to navigation systems for directing the movement of an object so that it will reach its intended destination, and more particularly to vehicle navigation systems searching for a movement path or guidance route of a ground mobile object based on map information to provide mobile-object operators with information concerning the route. The invention also relates to a vehicle navigation apparatus as enhanced with on-map searching of a surface target object and indication of the information thereof.
2. Description of the Related Art
As one navigation system, a vehicle navigation apparatus is described for example in Published Unexamined Japanese Patent Application (PUJPA) No. 61-194473. This vehicle navigation apparatus comes with a display device for visually indicating any part of a road map as desired by a user. The map displays on the screen the presentation of several conditions required to search for an intended facility that is presently set as a destination or target point at which the vehicle aims. Hierarchical selection of several steps of conditions may allow the user to finally identify the facility the user wants to reach.
The location of such identified facility is then displayed by use of an identification mark on the map display screen. In addition, one recommendable movement path or route from a present position is searched for by the navigation apparatus based on the map information to be displayed simultaneously. Note here that while the mobile object, here vehicle, is travelling along the path of such recommended guidance route, necessary surface environmental information may be given to the user by means of audible presentation schemes such as guidance voices.
With the navigation apparatus, it may happen that the user changes his or her mind on the movement route or at a nearby point of the vehicle's present position and would prefer to visit a facility other than the target place determined earlier, for example, a place to eat or to refuel. In the case where the user wants to stop at a facility excluding the target place, it is required that such temporal "stop-at" place be again designated through iterative search operations based on the map information. The search operations may be similar to those in the initial entry of target place under substantially the same search conditions, which may include designation genre or category.
The genre being designated may involve, for example, a gas station or restaurant. Since the objective to stop at such facility is clear, selection is limited in order to extract only those facilities which meet the objective. One example is that the objective of stopping at such place is to refuel the vehicle. If this is the case, genre designation is made to search for gas stations only. In this way, once the genre is designated, a plurality of facilities belonging to such genre will be found and extracted.
In the prior art navigation apparatus the linear distance toward each facility extracted is visually indicated on the display screen. Note, however, that any relative positional relation of the user's vehicle and the facility remains indeterminate before an image of the exact "stop-at" facility is displayed on the map display screen. More particularly, the related art fails on some occasions to specifically indicate the geographic position with relation to a recommended movement route. This makes it difficult for the user to promptly figure out which one of the presently displayed facilities perfectly matches his or her desires.
With respect to a second embodiment of the invention, various types of vehicle navigation systems are presently available which provide route guidance to assist a vehicle to arrive at a user's desired target place by searching for an optimum route thereto. When the user inputs a target place, the system searches for an optimal route to the target place from a present position of the vehicle as detected using GPS or gyro, and indicates on a display on or near the dashboard of the vehicle a map image including the optimal route and a mark indicative of the vehicle's present position. When the user begins driving the vehicle along the optimal route displayed, the system continues providing route guidance to the target place by informing the user of appropriate instructions as to which course should be chosen next at a position whereat the system determines that further guidance is needed. For example, while the vehicle comes closer, by a certain distance, to a road junction or intersection whereat the vehicle should turn to the right or the left, the system attempts to display an enlarged diagram of such intersection while informing the user of a recommended running direction by use of audible or visual indication schemes to thereby provide a proper guidance route leading to the target place. The system allows, during display of such enlarged intersection diagram, the user to check the running direction at the intersection by visually indicating the position of a "landmark" near the intersection with a mark on the map image as presently displayed. The landmark may be, for example, a mark or symbol of a bank, a convenience store, which facilitates the user to quickly assure that the user is at the intersection in question. In this respect, the map being displayed during the route guidance, based on a course searched by the system, is designed to provide a minimized amount of information to retain quality visibility while the user is driving the vehicle.
However, on the user's side, more information as to the environment near the vehicle's present position is increasingly demanded. There exists a tradeoff: increasing such additive information to be displayed on the map image may reduce the visibility as a whole. For example, the user may want to get information as to some eating houses or restaurants near the vehicle's present position. Alternatively, the user may want to know where the nearest facility of interest, such as a gas station is located. On such occasions, simply displaying all the information as required makes the map difficult to be observed.
One navigation system avoiding the problem is disclosed in PUJPA No. 61-194475, wherein a pattern display scheme is employed allowing the kind of related facilities displayable on a road map to be visually indicated using a pattern image at a predefined position on the screen of an associated display device. This may enable the user to display a pattern image of related facilities at certain positions on the map being displayed on the display device.
A significant disadvantage of the prior known system is that all the information is increased in amount causing necessary data storage devices to be complicated in structure and in architecture. More specifically, in cases where the system is arranged to separately store the guidance information data of landmarks, and the information data used to search for the user's desired facility around the vehicle's present position, for use in checking for the vehicle's running direction in the enlarged intersection diagram, the resulting amount of information to be stored increases resulting in more complexity as a whole. In some cases, it may be required that the search information data and guidance display data be redundantly stored which further increases complexity in the system arrangement. In particular, this will become more serious when the system is designed for information-rich midtown areas which come with an increased amount of data to be stored resulting in an increase in storage capacity of the system per se. This necessitates installation of extra add-in memory devices thus increasing the manufacturing cost of the system as a whole.